Enhanced oxidation of fluoroquinolones by visible light-induced peroxydisulfate: The significance of excited triplet state species

Recently, catalyst-free activation of peroxydisulfate (PDS) via visible light has been extensively investigated. However, the intrinsic relationship between the activation of PDS and the characteristics of pollutants has been largely ignored. This study reports that PDS activation by visible light without any artificial catalyst for the removal of fluoroquinolones (FQs), which reduced the adverse on ecological environment and human health concerns. Importantly, the mechanism of PDS activation by the excited triplet state of FQs ( 3 FQs*) was proposed. Experimental results demonstrated PDS could generate more ∙ OH with the existence of 3 FQs*. Meanwhile, the electron transfer pathways from FQs or 3 FQs* to PDS were studied. Both radical and non-radical oxidation reactions lead to the degradation of FQs in the Vis/PDS system. The degradation pathways and reactive sites were clarified by QTOF analysis and DFT calculations. Additionally, the degradation experiments of various contaminants demonstrated that the system showed excellent selective oxidation for FQs. • Transient absorption spectra and DFT calculations confirmed the existence of 3 FQs*. • A novel photoexcitation mechanism was investigated via fluorescence and phosphorescence spectra. • Unlike artificial photo-catalysts, this study provided other methods to activate PDS, such as visible light and excited state species.